Field of the Invention
The present invention relates to a positive photosensitive resin composition, a photo-curable dry film produced by using the positive photosensitive resin composition, a method for producing the photo-curable dry film, a layered product having the photo-curable dry film laminated on a substrate, a patterning process using the positive photosensitive resin composition or the photo-curable dry film, and a substrate obtained by the patterning process.
Description of the Related Art
As various electronic devices including a personal computer, a digital camera, and a mobile phone progress toward downsizing and higher performance, requirements are rapidly increasing for further downsizing, thinning, and higher density in a semiconductor device. Accordingly, it is desired to develop a photosensitive insulation material that can accommodate an increase in surface area of a substrate for the sake of higher productivity, and further can accommodate structures having fine concavity and convexity with a high aspect ratio on a substrate, in high density mounting technologies including a chip size package or a chip scale package (CSP) and a three-dimensional lamination.
As the above-mentioned photosensitive insulation material, a photo-curable resin composition has been proposed (Patent Document 1), in which the composition can be applied so as to give a wide range of film thickness by a spin coating method commonly used in the semiconductor device fabrication, be processed into a fine pattern using a wide range of wavelength, and be post-cured at low temperature into a top coat having excellent flexibility, heat resistance, electric characteristics, adhesiveness, reliability, and chemical resistance to protect electric and electronic parts. The spin coating method has an advantage that a film can be readily formed on a substrate.
The above-mentioned photo-curable resin composition for providing a top coat to protect electric and electronic parts is used with a film thickness of 1 to 100 μm on a substrate. However, there is a practical limit in the photo-curable resin composition because when the film thickness exceeds about 30 μm, its viscosity becomes too high to form a film on a substrate by the spin coating method.
Also, when the photo-curable resin composition is applied onto a substrate having an uneven surface by spin coating, it is difficult to form a uniform layer on the substrate. Because of this, the photo-curable resin layer tends to generate voids on the uneven part of the substrate, and thus, further improvements in planarity and step coverage have been desired. As the alternative coating method in place of the spin coating method, a spray coating method has been proposed (Patent Document 2). However, in principle, this method tends to readily cause defects such as height difference due to unevenness of the substrate, film loss at pattern edge, and a pinhole in recess bottom, and thus, the problems of planarity and step coverage still remain unsolved.
In recent years, in the high density mounting technologies including a chip size package or a chip scale package (CSP) and a three-dimensional lamination, a technology by which a fine pattern having a high aspect ratio is formed on a substrate, followed by laminating the pattern thus obtained with a metal such as copper, whereby rewiring from a chip, is very active. As the chip advances toward higher density and integration, it is strongly desired in the rewiring technology to reduce the line width of a pattern and the size of a contact hole for connecting between substrates.
Moreover, it is necessary that a pattern used for rewiring permanently exists between device chips, and the pattern material must have a cure ability and also serve as a top coat having excellent flexibility, heat resistance, electric characteristics, adhesiveness, reliability, and chemical resistance to protect electric and electronic parts.
From the background as mentioned above, a negative resist composition was assumed to be appropriately applied to the common lithography for obtaining a fine pattern, and suitable as the composition for the patterning process capable of processing a fine rewire and forming a top coat with excellent flexibility, heat resistance, electric characteristics, adhesiveness, reliability, and chemical resistance to protect electric and electronic parts.
However, if a negative resist composition is used to form a contact hole for connecting between substrates or wires and circuits in the three-dimensional lamination, thereby constituting a through electrode, the contact hole tends to be formed in a reversed tapered shape such that the upper aperture diameter is smaller than the lower aperture diameter, or to be formed in an overhang shape such that the upper aperture is extremely small. The reversed tapered shape and the overhang shape make the metal film formation by sputtering and the metal embedding by plating difficult. The preferable shape of the contact hole constituting a through electrode is a forward tapered shape such that the upper aperture is larger than the lower aperture.
Further, it is concerned that the negative resist composition reaches a limit of resolution in accordance with a pattern miniaturization expected to further progress in future. That is, the negative resist composition may cause an undissolved residue and a scum in the pattern bottom, and a footing profile in the pattern on the substrate e.g. when thickness of the covering film formed of the resist composition on the substrate is thick. These scum and footing profile are likely to cause problems including disconnection of an electric circuit and a wire during the rewiring process, so that it is necessary to suppress generation of such problems. However, it cannot be denied that these scum and footing profile become difficult to be resolved in the negative resist composition, as the miniaturization further progresses.
On the other hand, the negative resist composition that is capable of forming a fine pattern to be used for a rewiring process and is useful for a top coat to protect electric and electronic parts occasionally covers over a Cu wiring that has been previously processed on a substrate or over an Al electrode on a substrate. In addition, the substrates provided with a wire and an electrode include an insulating substrate such as SiN, which needs to be covered widely. However, adhesiveness between these substrates and a covering layer formed of the negative resist composition is not sufficient yet, so that there often occurs a problem that the covering layer formed of the resist composition is delaminated from the substrate.
Moreover, in patterning by using the negative resist composition useful for a top coat to protect electric and electronic parts, an organic solvent is used often as a developer in development. In this case, the exposed part becomes insoluble in an organic solvent developer by a crosslinking reaction or the like, while the unexposed part is readily soluble in the organic solvent developer, thereby obtaining a pattern.
However, there is an idea that development by the organic solvent developer is not desirable in view of treatment of waste liquid after development, load to an environment, and so forth. Moreover, the organic solvent developer is so expensive that development by an aqueous alkaline solution such as a 2.38% tetramethyl ammonium hydroxide (TMAH) aqueous solution, which is cheap and widely used in lithography patterning, is preferred.
In development using an aqueous alkaline solution such as a 2.38% TMAH aqueous solution, some negative resist compositions used in recent years have small difference in solubility in the developer between the exposed part and the unexposed part. In other words, the so-called dissolution contrast therebetween is sometimes small. When the dissolution contrast is small, it cannot be always expected to form a good pattern satisfying a demand of a fine pattern. In addition, when the dissolution contrast is small, there is a fear that a pattern cannot be formed on a substrate accurately according to a mask used in transferring and forming a pattern. Therefore, the resist composition and photosensitive resin composition requires the highest dissolution contrast as possible in the use of an alkaline developer, that is, it is required to enhance resolution.
Accordingly, drastic improvement of adhesiveness on a substrate is desired while not only maintaining the fine patterning ability in the rewiring technology required in accordance with the trends to higher density and higher integration of chips but also serving as a photosensitive material useful for a top coat to protect electric and electronic parts. Also, it is desired that a contact hole for forming a through electrode connecting metal wires has a forward tapered shape. In addition, wanted is prompt building up of the system in which patterning is possible by a widely used alkaline developer such as a 2.38% TMAH aqueous solution, further improvement in resolution can be expected, and a scum and a footing profile are not generated in the pattern bottom.